We aim to develop a targeted nanoparticle-based cancer therapy. We chose advanced prostate cancer (PCa) because androgen deprivation therapy (ADT), the only effective therapeutic option, fails after a relatively brief initial respone. Because of its high mortality rate, and significant impact on patient quality of life, novel treatment modalities for advanced PCa are highly important and much needed. The failure of anti-androgens is due, at least in part, to autonomous local testosterone production by PCa tumor cells. As a result, advanced PCa develops a unique requirement for cholesterol, which is a substrate for androgen biosynthesis. Cholesterol, insoluble in aqueous solution, is internalized via lipoproteins, specifically high density lipoproteins (HDL) in PCa. HDL and cholesterol uptake occur through the HDL uptake receptor, scavenger receptor B-1 (SR-B1), which is up-regulated in advanced PCa. We will employ the increased SR-B1 expression for PCa targeting with nanoconjugates to deliver gene targeted siRNA. We hypothesize that efficient systemic delivery of nucleic acid cargo can be facilitated by the robust and directed fabrication of biomimetic spherical HDL nanoparticles using a novel approach pioneered by our group. Recently, our group utilized a gold nanoparticle scaffold (AuNP) to generate biomimetic HDLs that recapitulate the size, shape, surface chemistry, and cholesterol binding properties of mature spherical HDLs. The resulting nanoparticles (HDL AuNPs) adsorb nucleic acids with high affinity. Initial in vitro and in vivo experiments show that these unique biomaterials are non-toxic, accumulate in the tissues that normally bind HDL, and function to regulate target gene expression. We propose to characterize and optimize the HDL AuNP conjugates loaded with siRNA and to test their properties in vitro and in preclinical model of prostate cancer. We expect that HDL AuNPs carrying siRNA will accumulate in the sites of SR-B1 expression, including in experimental PCa where SR-B1 is over-expressed, and efficiently deliver siRNA to PCa cells. Thus delivered, siRNA will block the expression of target gene(s). As a model target we chose the androgen receptor, a critical mediator of advanced prostate cancer. Project success will result in an effective and targeted siRNA therapy for advanced prostate cancer.